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Discussion Starter #1
Alright, from my search about the aux fan, there been plenty of post regarding it not turning on at all and such or other wise being in operable. My issue is the opposite, as it stays on in high speed mode when ever the car is running regardlss of temperature. From my understanding of how it suppose to work (and the way it worked in my past 560) is that it turns on when coolant reaches over 110 or so and when the AC is operating (like it does on the BMW e23). My fan stays on at high speed also, the AC compressor wont kick in even with pressure and coolant temperature is not even operating temp or in normal range of 80 or slightly above. (without it plugged in, the car does not over heat on a side note or even go much above 80 (difference is about minus 2 or 3 Cel. in normal operation.))

My guess is the temp sensor yet all the post about the temp sensor goign bad usually causes the fan to not operate at all or the fan to turn on when the temp sensor (the plug thing with blue plastic surround near the thermostat housing)is unplugged. In my car when the sensor is plugged in or not makes no difference as the aux fan stills run at high speed. Using a manual thermo, temp at radiator, block, coolant return hose from water pump and to thermostat is all within normal coolant range so no over heating or any other signs of over heating). coolant level is normal and has been consistant normal so no leaks or anything or other loss of coolant.
My bets guess is the prior mention coolant temp or what ever item sends the electical current to it which is...? or what fuse?

1988 MBZ 420SEL 4.2 V8 stock motor single air intake (last exhuast test was reading as good as new) Relative new radiator, alternator, master brake clylinder and related major brake parts and vaccuum hoses.)

The AC clutch does not appear to be locked up nor caked with with debris of time and the free pulley turns normal, and th wire is not frayed or other wise visable damaged, relay is good as been replaced with known working one even though the old one was never proven to be defective. Push button does it job proper, even though one vaccum pod are sticking aka kicking the bucket but are recieving proper signals and vaccum input. One pod (controls defrost door in default mode directs air to window defrot vent) does not holds vaccum and must be manually pushed to operate door. Main cooling fan (clutch fan) works as intended.


So in short, is it just a malfunctioning of thetemperature sensor that cause fanto stay on high speed or is it that the temp sensor is not recieving proper volt imput and where or what item does it gets the volt imput from so that can be checked for proper function and possibly ruled out or repaired.
 

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Someone probably jumpered the fan usually because they switched to R134a. There's no way to tell where they did it, maybe at the relay.
 

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Discussion Starter #3
gosh I hope they didnt switch to R134a as one, there ino R134 sticker, the low pressure input is still R-12 connection, same with high, which means if they went R134a then it looks like crack job.


There is a leak test sticker and according to the shop that did it, their records indicate no leaks was found.

Now that you mention it, that means I have no idea or means to tell what exactly was in there, bugger. Hell I dont even know if it's mixed. Now that you mention it, not even sure if they thought of changing the pressure switches or what.

and I hope they didnt jumpered anything as nothing is more annoying than people trying ot bypass stuff and mess other things up because of shoddy electrical work.


So since the sytem might have been r134a or mighthave still been r12 how do or where is the best place to go and get the system cleaned completely out as seems this is the best place to start. Start fresh, then go from there. I'll probably buy a new drier and the switches anyways.

Then the next thing is to see and check all fan circuits for any type of jumping. I'll start at fuse, then check around resistor, and everything in between. From the reciver drier near connector to the fan, it's stock wire and no signs of tamper.

but assuming the system is stock r12 and no crazy jumps are in place, what could it be.
 
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